SSL – insecure elements

Just looking for some help with using https on a multisite. I have https running completely fine, but I would just like to find out how to make a change so I no longer have to use a plugin. A plugin like the WordPress-https is too large for the simple thing I need to fix.

I have SSL forced everywhere, frontend and admin

# htaccess Https everywhere
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

/* and wp-config */
define('FORCE_SSL_ADMIN', true);

The only thing that needs fixing are the insecure elements such as images with http in the url. I know how this can be fixed without using an https plugin but it means I have to make manual changes to each sub site:

I can fix these insecure elements on my main site (mysite.com), by changing http to https for my siteurl and home url. The same thing can be done to fix these insecure elements on all sub sites again replacing http with https for each sub site’s siteurl and home url values. But because I allow users to create sites on my multisite I need this done automatically.

Basically, I’m trying to find out how to make the values for siteurl and home url have https in them automatically instead of http, for each sub site.

Any help appreciated